Lazy Photographers
Basically, it's lazy photographers. There are many ways to get good photos of guns, but you have to work at it.
There are nifty ways to get the shot with good lighting and no shadows, or to put the shadows where you want. But you have to work at it.
It is much easier now that we have digital cameras. With film, if we didn't have a Polaroid back, we had to guess, bracket, shoot a lot, and wait for the film to be developed.
Hint. Keep modeling clay handy for getting guns to stay where you want.